Correctly interpret /etc/ssh_config Authentication settings based on openssh /etc/ssh_config system defaults.

This will allow for correct interpretation of system wide defaults. Rather than overwriting ALL default auth_methods when a user has "PasswordAuthentication yes" in their /etc/ssh_config you should simply leave the default auth_methods as is as they already contain "password". You should not edit the defaults unless a user has explicitly set "PasswordAuthentication no". The inverse also applies to "HostbasedAuthentication" or hostbased auth_methods defaults. You can produce the incorrect behavior with the current 2.7.0 gem by editing the /etc/ssh_config on your machine and setting "PasswordAuthentication yes" this will cause publickey based auth to be disabled. That is not how openssh client config is intended to be interpreted. Explicitly enabling PasswordAuthentication should not implicitly DISABLE publickey based auth. This pull request addresses this misinterpretation.